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Fekir sought to restore parity with a shot from the centre of the box, only to be denied by Montpellier stopper Geoffrey Jourdren down at his bottom-right corner.
The away side slowly grew dominant and they equalised when Abdelhamid El Kaoutari brought down Fakir in the box, leaving Lacazette to convert the penalty.
HSC offered little going forward in the second half, but Barrios stood out again with a superb long-range shot that almost surprised Lopes, who saved well.
Les Gones looked to cement the victory with just under 20 minutes to play when Fekir bagged his brace, handing Gourcuff his second assist of the game.
Lyon added another goal in injury time to send out a message to both Paris Saint-Germain and Marseille, and it came through youngster Corentin Tolisso who tucked home from close range.
The fireworks did not stop there, however, as Lacazette returned to secure his second of the night, finishing from Mohamed Yattara's cross to leave the final score at 5-1.